POCs inhibit ovulation by suppressing the luteinizing hormone (LH) surge, which blocks egg implantation by producing an atrophic endometrium. A secondary mechanism of contraception is the production of a thickened cervical mucus which provides a mechanical barrier to sperm motility.^19* Drospirenone is available as a 24/4 formulation. The norethindrone formulations are 28-day packs meant for continuous dosing. The effectiveness of oral POCs varies by progestin type. Norethindrone’s typical use failure rate is approximately 5% compared to 1.8% for drospirenone. Norethindrone uses approximately 33% of the progestin dose in COCs (0.35 vs. 1 mg), while drospirenone-containing oral contraceptives use 33% more (4 mg vs. 3 mg).^51,52 

Table 8 – Advantages & Disadvantages of POCs^48*

Side effects include breakthrough bleeding, menstrual irregularities, prolonged bleeding, erratic menstrual intervals, vaginal dryness, and amenorrhea. Amenorrhea is more common with the long-acting forms of progestin than the oral formulations.

POCs do not appear to cause alterations in mood.⁵³ A 12-month observational study of 102 women using progestin orally or via IUD had a nonsignificant increase in weight and a slight increase in fat mass compared to controls.⁵⁴ POCs do not seem to increase insulin resistance in women except for lactating women with a history of gestational diabetes. Compared to COCs, POCs were associated with a RR of 2.87 (95% CI 1.57 to 5.27) to cause hyperglycemia. These patients should have their glucose monitored while on POC treatment.⁵⁵ Sonographic imaging indicates that follicular cysts occur more frequently in POC users vs. nonhormone users; however, these tend to shrink over time. No interventions are necessary, but if women have cystic pain, they can be switched to another form of birth control.⁵⁶ A systemic review found that POC therapy is not associated with an increased risk of stroke, VTE, or MI.⁵⁷ POCs have little impact on blood pressure.⁵⁸ Progestin-only formulations have minor effects on lipid profiles.^37* A case-control study evaluated the risk of POCs and breast cancer and found no association with elevated breast cancer risk.⁵⁹ Daily POC use is associated with a reduced risk of endometrial cancer.⁶⁰ Data on efficacy in obese women is not sufficient to make a recommendation.

The pharmacist should counsel the patient to take POCs every day at the same time within a 3-hour window. POCs may be started at any time in a woman’s menstrual cycle; however, if initiated > 5 days after menses has begun, a backup method or abstinence is recommended for two days to prevent breakthrough pregnancy. Return to fertility occurs sooner with POCs than COCs, with an average time of one month. When switching from a POC to an IUD, implant, or injection, another method of contraception should be used for seven days to prevent pregnancy. Changing to other forms of contraception do not require a backup method.